Nonlinear optical waveguide device

ABSTRACT

A waveguide is formed by performing epitaxial growth of β-BaB 2  O 4  on top of α-Ba 1-x  Sr x  B 2  O 4  (where 0.04≦x≦0.10). A nonlinear optical waveguide device using β-BaB 2  O 4  can output a highly converted laser beam.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a nonlinear optical waveguide device which uses β-BaB₂ O₄ thin film on an α-Ba_(1-x) Sr_(x) B₂ O₄ substrate.

2. Description of the Prior Art

β-BaB₂ O₄ has a relatively high nonlinear optical coefficient and is transparent up to the ultraviolet region, which is superior as a crystal for harmonic generation. In the past, however, it was only used as a bulk single crystal. Used in this way, the input power to the device was increased making it possible to increase the optical energy density.

For nonlinear optical devices which used β-BaB₂ O₄ being transparent up to the ultraviolet region, an optical waveguide was necessary in order to increase the optical energy density without increasing the input power to the device.

SUMMARY OF THE INVENTION

An object of this invention is to provide a nonlinear optical waveguide device which uses β-BaB₂ O₄ that is capable of obtaining an output beam of a high optical energy density using a low output light source.

The aforementioned object of this invention is effectively accomplished by providing a nonlinear optical waveguide device comprising a substrate of α-Ba_(1-x) Sr_(x) B₂ O₄ wherein the subscript x satisfies the following relation: 0.04≦x≦0.10, and a wavelength formed by performing epitaxial growth of β-BaB₂ O₄ thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The applicant has found that when the Ba of β-BaB₂ O₄ is partially substituted with Sr, α-Ba_(1-x) Sr_(x) B₂ O₄ wherein the subscript x satisfies the following relation: 0.04≦x≦0.10, as shown in Table 1, the composition has a refractive index that is low as compared with β-BaB₂ O₄. If a thin film is formed by performing epitaxial growth of β-BaB₂ O₄ on an α-Ba_(1-x) Sr_(x) B₂ O₄ substrate (0.04≦x≦0.10), it is possible to form an optical waveguide using the difference in the refractive indices of the two.

                  TABLE 1                                                          ______________________________________                                                         Refractive index                                                               1.064 μm                                                                            0.532 μm                                                            wavelength                                                                             wavelength                                             ______________________________________                                         β-BaB.sub.2 O.sub.4                                                                    n.sub.o  1.6570    1.6741                                                      n.sub.e  1.5390    1.5541                                         α-Ba.sub.0.96 Sr.sub.0.04 B.sub.2 O.sub.4                                             n.sub.o  1.6426    1.6597                                                      n.sub.e  1.5246    1.5397                                         α-Ba.sub.0.94 Sr.sub.0.06 B.sub.2 O.sub.4                                             n.sub.o  1.6444    1.6611                                                      n.sub.e  1.5260    1.5411                                         α-Ba.sub.0.93 Sr.sub.0.07 B.sub.2 O.sub.4                                             n.sub.o  1.6444    1.6615                                                      n.sub.e  1.5264    1.5415                                         α-Ba.sub.0.92 Sr.sub.0.08 B.sub.2 O.sub.4                                             n.sub.o  1.6446    1.6617                                                      n.sub.e  1.5266    1.5417                                         α-Ba.sub.0.90 Sr.sub.0.10 B.sub.2 O.sub.4                                             n.sub.o  1.6459    1.6630                                                      n.sub.e  1.5279    1.5430                                         ______________________________________                                          n.sub.o : Refractive index for ordinary ray.                                   n.sub.e : Refractive index for extraordinary ray.                        

Accordingly, for a nonlinear optical device which uses β-BaB₂ O₄ being transparent up to the ultraviolet region, by creating a thin film waveguide structure, the propagation of light can be controlled inside the film, and thus the optical energy density of the output beam can be increased easily even if the input power is small. Thus, it is possible to obtain a highly converted laser beam having a short wavelength and which can use a low output light source.

Following, an embodiment of this invention will be described.

BaCl₂ ·2H₂ O (0.96 mol), SrCl₂ ·6H₂ O (0.04 mol) and H₃ BO₃ (2.00 mol) were dissolved in 2 liters of water and adjusted to a pH of 12 to precipitate Ba₀.96 Sr₀.04 B₂ O₄ ·4H₂ O. The resulting precipitate was then fired at 800° C. for 10 hours to obtain α-Ba₀.96 Sr₀.04 B₂ O₄. This powder was then put into a platinum crucible and an α-Ba₀.96 Sr₀.04 B₂ O₄ single crystal was grown using a normal single crystal pulling high frequency furnace. The pulling process was performed using a seed revolution of 20 rpm and a pulling speed of 3 mm/h in an atmosphere of air, and the direction of growth was along the c axis. The grown crystal was cut along the C plane and was processed to be used as a substrate.

The β-BaB₂ O₄ powder was made by dissolving 1 mol of BaCl₂ ·2H₂ O and 2 mol of H₃ BO₃ in 2 liters of water and adjusting the pH to 12 to precipitate BaB₂ O₄ ·4H₂ O and then firing the resulting precipitate at 800° C. for 10 hours.

The β-BaB₂ O₄ powder was used as a fusing material for liquid phase epitaxial growth, and the α-Ba₀.96 Sr₀.04 B₂ O₄ of the Z plane was used as the substrate in making a thin film of βBaB₂ O₄ with a film thickness of 1 μm.

A 0.532 μm SHG beam was obtained from the outputting end of this thin film planar waveguide by inserting the LD pumped 1.06 μm Nd: YAG laser beam.

The same procedures as used in the above embodiment are repeated to give α-Ba₀.94 Sr₀.06 B₂ O₄, α-Ba₀.93 Sr₀.07 B₂ O₄, α-Ba₀.92 Sr₀.08 B₂ O₄ and α-Ba₀.90 Sr₀.10 B₂ O₄ in place of the α-Ba₀.96 Sr₀.04 B₂ O₄ used as the substrate and to make a thin film of β-BaB₂ O₄ having a thickness of 1 μm thereon. For the thin film planar waveguide thus obtained, the highly converted laser beam as mentioned in the above embodiment can be obtained from the outputting end of the waveguide.

As was described above, this invention makes it possible to obtain an output beam of high optical energy density with low input power, and it is possible to provide a nonlinear optical waveguide device which uses β-BaB₂ O₄. The nonlinear optical waveguide device can be utilized in a field of a laser processing, an optical disc memory or read, or the like. 

What is claimed is:
 1. A nonlinear optical waveguide device comprising a substrate of α-Ba_(1-x) Sr_(x) B₂ O₄ wherein the subscript x satisfies the relationship: 0.04≦x≦0.10, and a waveguide of β-BaB₂ O₄ epitaxially grown therein.
 2. The nonlinear optical waveguide device as defined in claim 1 wherein said waveguide is a thin film planar waveguide.
 3. A nonlinear optical waveguide device comprising a substrate of a α-Ba_(1-x) Sr_(x) B₂ O₄ having a refractive index of 1.6426 to 1.6459 at 1.064 μm wavelength of ordinary ray and a refractive index of 1.5246 to 1.5279 for extraordinary ray, wherein the subscript x satisfies the relationship: 0.04≦x≦0.10, and a waveguide of β-BaB₂ O₄ epitaxially grown therein.
 4. The nonlinear optical waveguide device as defined in claim 3 wherein said α-Ba_(1-x) Sr_(x) B₂ O₄ has further a refractive index of 1.6597 to 1.6630 at 0.532 μm wavelength of ordinary ray and a refractive index of 1.5397 to 1.5430 for extraordinary ray.
 5. The nonlinear optical waveguide device as defined in claim 3 wherein said waveguide is a thin film planar waveguide. 